PROJECT SUMMARY Alzheimer?s Disease is the 6th leading cause of death in the U.S, affecting 10% of seniors over the age of 65. Despite the myriad Alzheimer?s Disease therapeutics targeting the production and clearance of the ?-Amyloid (A?) peptide, an effective cure is yet to be identified. The current, commonly accepted amyloid model of this disease only seeks to understand the properties of two predominant isoforms of A? - with 40 or 42 amino acids. However, plaques isolated from the brains of Alzheimer?s patients contain a variety of A? peptides and other proteins. The long-term objective of the proposed research is to elucidate the mechanisms by which A? and its variants contribute collectively to the pathology of Alzheimer?s Disease. A C-terminal fragment of A?, p3, has been described as soluble and void of amyloidogenic properties since its discovery, despite minimal scientific evidence to support this. I propose to synthesize and characterize the aggregation and mechanism of toxicity of p3 to elucidate its role in amyloid fibril formation. My hypothesis is that the p3 fragment forms amyloid fibrils capable of imparting drastic changes on the oligomerization of the well-studied 40 and 42 length A?. The current amyloid model can be significantly improved by understanding the collective contribution of all A? peptides through their kinetic interactions. Aim I will provide insights on how p3 aggregates into amyloid fibrils and how that pathway deviates from A? with the use of kinetic assays, antibodies and photo-induced crosslinking. Aim 2 will create a more heterogenous model for the aggregation of amyloid peptides into fibrils through coincubation and seeding assays with p3 and A?. Aim 3 will provide advances in our understanding of how p3 exerts its toxicity on cells and how that pathway differs from that of A?. The mechanism of p3 toxicity will be explored with various biorthogonal cellular uptake methods and apoptosis assays. Completing the listed aims will elucidate the role that p3 plays in the kinetics of amyloid plaque formation and cell toxicity. By providing key insights into the aggregation properties and biological activity of p3, the proposed work will clarify how p3 interacts with A?. Ultimately, I expect the results to modify and refine the currently accepted amyloid model, providing a more comprehensive understanding of the pathology of Alzheimer?s Disease.